1. Field of the Invention
The present invention relates to an automated shift control device for a straddle-type vehicle.
2. Description of Related Art
Vehicles including an automated shift control device for automatically switching speed change gears are known. A typical automated shift control device includes a transmission having pairs of speed change gears with different transmission gear ratios and a gear selecting mechanism for selecting a pair to transmit power; a shift actuator for driving the gear selecting mechanism; and a shift power transmission mechanism for transmitting power from the shift actuator to the gear selecting mechanism.
In a transmission having dog gears, the gears sometimes may not engage or may not disengage smoothly during gear shifting. When this occurs in a foot-operated type transmission in which the gear selecting mechanism is driven via a shift pedal, for example, operation by foot may be repeated several times so that the gears engage or disengage to complete the gear shifting operation. However, in order to automatically perform such operation by means of an automated shift control device, an input from the shift actuator must be appropriately controlled in a complicated manner. On the other hand, when a situation in which the gears may not smoothly engage or disengage is left, there is a problem in that while the shift actuator is energized, rotation of the shift power transmission mechanism is restrained and therefore the shift actuator cannot rotate, thereby overloading the shift actuator.
Japanese Patent No. 3044498 proposes an automated shift control device in which a coil spring is disposed between the shift actuator and the shift drum of the gear selecting mechanism. According to Japanese Patent No. 3044498, when the shift actuator is energized but rotation of the shift power transmission mechanism is restricted, the coil spring elastically deforms, thus preventing overload of the shift actuator.
However, in order to prevent overload of the shift actuator by using elastic deformation of the coil spring, an elastic modulus of the coil spring must be set smaller. In other words, a compressive load when the coil spring elastically deforms (“compressive load of the coil spring”) must be set small enough so that operation of the shift actuator is allowed when the shift power transmission mechanism stops.
However, as the compressive load of the coil spring becomes smaller, it becomes more difficult to disengage the dogs of the dog gears. Accordingly, another problem arises in that when the compressive load of the coil spring is set to be smaller, the engaged gears may not be smoothly disengaged, and the time from beginning to completion of the gear shifting operation may be increased.
On the other hand, when the compressive load of the coil spring is set to be larger, overload of the shift actuator cannot be suppressed as much as has been expected. Therefore, torque of the shift actuator must also be suppressed in order to prevent overload.
However, suppression of the torque of the shift actuator also reduces rotational speed of the shift actuator, and may increase the time from beginning to completion of the gear shifting operation.